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From: adrianw@guinevere.st.nepean.uws.edu.au (Adrian Whichello)
Newsgroups: comp.sys.apple2
Subject: Re: Apple II+ power supply woes
Date: 13 Aug 1994 17:09:31 +1000
Organization: University of Western Sydney
Lines: 40
Message-ID: <adrianw.776761728@lancelot.st.nepean.uws.edu.au>
References: <adrianw.776562249@lancelot.st.nepean.uws.edu.au>
NNTP-Posting-Host: 137.154.148.15
Keywords: power supply woes
adrianw@kay.st.nepean.uws.edu.au (Adrian Whichello) writes:
>Hi Netland
>I have an old 2+ which runs the model railway, among other things.
>Last week it's power supply gave up. I wasn't there at the time,
>I've found that leaving the computer permanently switched on is
>good insurance - the power supplies tend to die between cycles if
>eft off for long periods. Anyway, I opened it up and found that
>an electrolytic had swelled up so much that it had torn it's connections
>out of the circuit board. I replaced it, but all the power supply
>wants to do now is go click click click ie it won't oscillate
>properly. It does this if plugged into the motherboard or not.
>Any suggestions about what else could be wrong. I'm not wild
>about diving into a circuit that is connected directly to the
>house supply without some clues.
>Adrian.
>ps surely this must be a FAQ by now - I have several old supplies
>that are dead for one reason or another.
Hi Netland
had a go at the power supply over the weekend. I was successful, because
I typed this on the Apple. There was nothing wrong with the bridge rectifier
and input side - there was over 300V on the collector of the big transistor.
None of the inductors had burnt out and all the diodes and transistors checked
out OK with a simple multimeter check. In fact nothing looked wrong at all,
physically. There was just hardly any (~0.5VDC) voltage on the output side.
I was getting desperate! I decided to check out the voltage reference section
- I faked 5VDC (from the bench power supply) on the anode of the TL-431C and
up came the power! So then the penny dropped, the capacitor the temporarily
shorts out the 4.7K 1% resistor at power on wasn't doing it's job. I replaced
it and away we went, all systems go. Anyone else found this?
Adrian.